Water repellent filter seal

Abstract: A filter seal (5) which is capable of passing oil and of removing contaminations from said oil comprises a layer of filter material (10) which is oil-permeable. Moreover, the filter material (10) is water repellent, such that water droplets are rejected. In order to also reject the smaller water particles e.g. water molecules, furthermore hydrophilic means are provided for absorbing small water particles.

Description: The invention relates to a filter seal which is capable of passing oil and of removing contaminations from said oil, comprising a layer of filter material which is oil-permeable. Such filter seals are for instance applied in rolling element bearings for use in an oil splash environment, e.g. in a gear box. In order to provide an appropriate lubrication, oil may enter the bearing space through the filter seal, whereby contaminations such as wear particles from the moving components such as tooth gears may be filtered out. An example of such filter seal is shown in GB-A-1319953. Apart from wear particle contaminations, water contamination is a matter of concern as well. Water contaminant in oil exerts a detrimental effect on bearing life in particular. The negative effects thereof have often been attributed to the mechanism of hydrogen embrittlement. The object of the invention is therefore to provide a filter seal which is capable of removing any water contaminant which is contained in oil. This object is achieved in that the filter material is water repellent. Any small water droplets or water particles are rejected by the water repellent nature of the filter material. The pressure required to force such water droplets through the filter material depends on the surface tension and inversely on the size of the filter pores. These properties of the filter material are selected in such a way that at the prevailing pressure conditions no ingress of water will take place. Although the above water repellent filter material is suitable for removing the bulk of water contained in the oil, nevertheless some very tiny water particles or water molecules might still pass through. In order to prevent such particles or even molecules from entering the bearing space, also hydrophilic means may be provided. Any water particles or molecules which might pass through the water repellent filter layer, are now absorbed by the hydrophilic means and are there kept from entering the protected area, i.e. the bearing space. Preferably, hydrophilic chemicals are grafted onto the surface of the layer of filter material. In order to obtain the best effect, the hydrophilic chemicals are situated at the side of the layer of filter material facing away from the contaminated oil. In another embodiment, the hydrophilic chemicals are incorporated into filter matrices. The filter material is preferably coated with a water repellent substance having a high contact angle. The filter material may be a metal mesh or a microporous polymeric material. The invention will be explained further with reference to an embodiment shown in the drawings. Figure 1 shows a rolling element bearing provided with a filter seal according to the invention. Figure 2 shows a cross-section, on an enlarged scale, of the filter seal according to the invention. A rolling element bearing 1 has an inner bearing space 2 which is delimited by outer ring 3, inner ring 4 and filter seal 5. The inner bearing space contains a number of rolling elements 6, held in cage 7. The rolling element bearing 1 is contained in a housing which is provided with an amount of oil 8. The housing may for instance be a gear box. In service, the oil 8 is splashed by the action of the gears, which means that oil droplets splash onto the bearing 1 and the filter seal 5. Thereby, oil may enter the inner bearing space 2 via the sealing element 9 of filter seal 5. Figure 2 shows, on an enlarged scale, this sealing element 9 in cross-section. It consists of a porous filter element 10, for instance a microporous membrane. Any water droplets contained in the oil are rejected by the membrane 10, as indicated by arrow 11. This rejection of water droplets is caused by the water repellent coating applied to the surfaces of membrane 10. Very small water particles, for instance water molecules, may however penetrate membrane 10. In order to avoid the ingress of such very small water particles into the inner bearing space, a hydrophilic layer 14 is provided. Any water molecules which cross the membrane 10, are adsorbed in said hydrophilic layer as indicated by arrow 12. Thus, the inner bearing space 2 is protected very well against penetrating water or even water molecules, in such a way that only clean oil is passed, as indicated by arrow 13.

Claims: Filter seal which is capable of passing oil and of removing contaminations from said oil, comprising a layer of filter material which is oil-permeable characterised in that the filter material is water repellent. Seal according to claim 1, in which hydrophilic means are provided for absorbing small water particles. Seal according to claim 2, in which hydrophilic chemicals are grafted onto the surface of the layer of filter material. Seal according to claim 3, in which the hydrophilic chemicals are situated at the side of the layer of filter material facing away from the contaminated oil. Seal according to claim 3 or 4, in which the hydrophilic chemicals are incorporated into filter matrices. Seal according to any of the preceding claims, in which the filter material is coated with a water repellent substance having a high contact angle. Seal according to any of the preceding claims, in which the filter material is a metal mesh or a microporous polymeric material.

Inventors: WAN GEORGE TIN YAU, WAN, GEORGE TIN YAU
Applicants: SKF IND TRADING & DEV, SKF INDUSTRIAL TRADING & DEVELOPMENT CO, B.V.
Application year: 1994
Main classification: F16C33
IPC codes: F16C33, B01D17, F16N39